Off-highway wheeled vehicles are used for utility as well as recreation. Sometimes referred to as off-road vehicles, these vehicles are useful in agriculture, construction, hunting/fishing, military, search and rescue, as well as other industries.
All-terrain vehicles (ATV's) are a specialized type of wheeled off-highway vehicle, characterized by broad, low-pressure tires, a seat to be straddled by the operator, and handlebars for steering. Utility vehicles are an additional subset of off-highway vehicles, often characterized by low-pressure tires, seating for the operator and one or more passengers, a steering wheel, and typically a cargo bed over the rear wheels. A roll bar or enclosed cab may be included on utility vehicles. Some utility vehicles incorporate a 6-wheel configuration having an additional rear axle. Various attachments and implements can be used with ATV's and utility vehicles for specialized tasks.
ATV's and utility vehicles are suited for travel over firmer off-road terrain such as grass, dirt, gravel, and shallow mud and snow. However, these vehicles are typically not capable of traversing more challenging loose terrain such as soft mud, sand, deep snow or even water, due to their relatively low ground clearances. Often, in such loose terrain, an ATV or utility vehicle may sink or become high centered and thereby become immobilized.
The use of tracks on ATV's and utility vehicles allows greater mobility in more challenging terrain such as loose terrains like soft mud, sand, or snow. Different versions of track arrangements are described, for example, in U.S. Pat. Nos. 6,615,939, 6,095,275, and 6,904,986. Unfortunately, such track assemblies typically must be installed in place of the wheels, making it a time-consuming process to switch from wheels to tracks. While useful in certain applications, tracks also have a number of disadvantages. Track assemblies are heavier than wheels and tires and have a much larger contact area, thereby negatively affecting the speed of the vehicle, as well as slowing steering response. Performance on dry or paved surfaces is poor, and sustained operation on paved surfaces rapidly wears out the tracks. Further, tracks offer little to no improvement when traversing water as compared to conventional wheeled configurations. Track assemblies are also mechanically complex, having many moving parts that are susceptible to damage or wear. The large contact area of tracks makes them difficult to free in the event they become frozen to the ground. In addition, track assemblies are prohibitively expensive for a large majority of ATV and utility vehicle owners.
Another approach to increasing mobility of off-highway vehicles over difficult terrain is to add an additional wheel on each axle hub. The footprint of the dual-wheel configuration is approximately doubled, resulting in improved performance over certain kinds of loose terrain. Different examples of dual wheel arrangements are described, for example, in U.S. Pat. Nos. 4,220,372, 6,062,651, 6,068,346, and 7,040,713. However, similar to track assemblies, the weight of the added wheels negatively affects vehicle performance. A single ATV tire weighs between 10 and 30 pounds, and the addition of a wheel, tire, and mounting hardware can add over 50 pounds per corner of the vehicle. This amount of added weight decreases the top speed of the vehicle, decreases acceleration, makes steering more difficult, as well as increasing turning radius. Further, the auxiliary wheel of a dual wheel arrangement typically is not covered by the vehicle's fenders, exposing the operator of the vehicle to dirt and debris flung off of the wheels.
A need exists, therefore, for improved devices and methods to allow off-highway wheeled vehicles to operate more effectively in loose terrain without the use of tracks or additional wheels.